Fixed a small bug that caused event leaking between successive RPC
invocations on the RPC server.
Addressed some annoying metadata propagation issues.  Since localization
requests and responses are sent via heartbeat, have to append individual
XTraceMetadata with each request and response.
Added some last little bits of xtracecontext passing between threads. 
Now just need to finish up the Mapper/Reducer/Task metadata propagation
Added ids to the agent of a statemachine to disambiguate different ones
I think I have the StateMachine causality correctly represented now.
Removed superfluous logging statement